1,720,989 research outputs found
Modelling Artificial Ecosystem Selection: a preliminary investigation
Full text linkThe ability of whole ecosystems to respond to selection has recently been demonstrated in artificial selection experiments, (Swenson et al 2000a, Swenson et al 2000b). As well as having wide-ranging practical applications, this result significantly broadens the application of theoretical concepts of the mechanisms of heritability and variation in biological systems. Simulation models have the potential to be useful tools for the investigation of these issues. Whilst related simulation work exists (Ikegami 2001, Wilson 1992), ecosystem-level selection itself has yet to be modelled. This paper presents such a model, in which ecosystems are modelled as generalised Lotka-Volterra systems and are subject to a generational selection process. A positive response to selection for diversity is demonstrated, with the only sources of variation being sampling errors arising when 'offspring' ecosystems are produced
What can artificial life offer the development of methodologies in the field of socio-ecological sustainability? (abstract).
No full textSystems Aikido: a novel approach to managing natural systems
No full textThe potential of new technologies which emulate or exploit the unique properties of living systems is widely lauded. Such technologies however, create new engineering challenges which must be addressed before they can become broadly utilised (see for example, Braha et al. (2006); Bedau et al. (2010); Penn (2008)). Additionally, many pressing challenges for society today are inherently concerned with gaining a better ability to understand and manage interacting living or life-like systems upon which we rely. Well-documented examples include climate change, agricultural sustainability, city dynamics, demographic change and chronic infections. Problems in all these areas demand a better ability to manage complex biological systems than is currently available.Conventional approaches to working with biological systems are, for the most part, brute force, attempting to effect control in an input and effort intensive manner and are often insufficient when dealing with the inherent non-linearity and complexity of living systems. Biological systems, by their very nature, are dynamic, adaptive and resilient and require management tools that interact with dynamic processes rather than inert artifacts. Our novel engineering approach which aims to exploit rather than fight those properties, presents a more efficient and robust alternative. Its essence is what I will call systems aikido, the basic principle of aikido being to interact with the momentum of an attacker and redirect it with minimal energy expenditure, using the opponents energy rather than ones own. In more conventional terms, this translates to a philosophy of equilibrium engineering, manipulating systems own self-organisation and evolution so thatthe evolutionarily or dynamically stable state corresponds to a function which we require.I will discuss how we might move from this philosophy to a practical methodology for management of living systems and technologies, covering a variety of approaches: Designing-in of tools for adaptive management given unexpected indirect effects and continuous adaptation of living components; identification of appropriate points of intervention in particular systems; and methods for steering adaptive systems by altering either the fitness landscape which they experience or the attractor structure of their dynamics. Filling fitness valleys to escape local optima; expansion of basins of attraction of difficult to access, but favourable attractors and manipulating the effective level of selection within the system.Detailed illustration is provided by a practical application: Manipulating the level of selection within bacterial biofilms, such that stable community species and genetic composition corresponds to a community function which we require (Penn et al. (2008b,a)). Different levels of selection produce particular types of community composition. Higher-level selection promotes co-operation and synergy useful for efficient bioremediation and bioproduction, whereas encouraging lowerlevel selection might allow us to engineer a tragedy of the commons in problematic bacterial communities. I will present methodology and results from ongoing experimental work with Psuedomonas aeruginosa biofilms in which direct or indirect manipulation of parameters affecting group structure and dispersal mechanisms modify the effective level of and hence response to selection. And will describe approaches to increase the robustness of the engineered communityFinally I will contrast this methodology with a spectrum of more or less brute-force interventions, from traditional biofilm engineering approaches to imposition of higher-level selection( Swenson et al. (2000b,a); Penn (2006))
The Role of Non-Genetic Change in the Heritability, Variation and Response to Selection of Artificially Selected Ecosystems
No full textA response to selection on the level of the ecosystem has been demonstrated in artificial selection experiments, and poses interesting challenges to concepts of heritability, variation and phenotype in biological systems. We use ecosystems modeled as Lotka-Volterra competition systems, and subject to an ecosystem-level selection process, to illustrate and discuss the potential, and possible mechanisms, for ecosystem-level evolution without genetic change of the component species. A limited positive response to selection is demonstrated by the selection of alternative stable ecosystem states
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Can individual selection favour significant higher-level selection? (abstract)
No full textHow do new evolutionary units, supporting higher levels of functional organisation, arise from existing evolutionary units? The adaptive transformation of co-adapted species into new units, as in the major evolutionary transitions, is centrally implicated in the evolution of complexity but has proved very problematic for current evolutionary theory and understandably elusive in ALife. We investigate the evolution of new evolutionary units via individual adaptation in a multi-species ecosystem by modelling symbiotic associations that cause interaction probabilities to deviate from a freely mixed condition. It is well known that assortative grouping supports group selection in a well-defined sense, thus it is no surprise that enabling such associations will introduce some group selection effects. However, what form will this take when the control of such grouping is under individual adaptation? We tackle this by comparing the ecosystem attractors of the initial freely mixed system to those of the same system given the evolved association probabilities. In general we find that self-interested adaptation of associations tends to only reinforce species combinations that were already stable before the associations — which seems rather uninteresting. However, if the species densities of the ecosystem are occasionally perturbed whilst associations are developing this causes the system to visit different attractors and allows multiple, possibly incompatible, associations to be selected for in different contexts. Under these conditions, even when the attractors of the final system already existed as attractors in the freely mixed system, competition between different combinations of species enlarges basins of attraction that lead to fit combinations at the expense of those that lead to less fit combinations. Thus, after the associations have evolved, a fit combination of species may be favoured in the niche that is constructed by the action of its association preferences, even if each species involved would be individually unfit if the system were freely mixed. These findings show that evolved higher-level selection can have significant effects even when the new units result from the self-interest of the constituent sub-units. They also suggest that evolved complexes observed naturally may appear to be merely the result of individual selection because they are supported by individual self-interest, but in fact the reason that this complex persists and not some other is due to competition among species combinations. Nonetheless, in small systems these mechanisms do not produce higher levels of complexity than those which occurred without evolved associations because the configurations that result were already visited in the initial freely-mixed system. However, we find that in large complex ecosystems with many local attractors, evolved associations naturally generalise over the relatively few attractors that are visited, enlarging attractors for fit species combinations even before they are visited. An idealisation of these processes has been shown to be far superior to conventional evolutionary algorithms on a fairly general class of difficult optimisation problems. This self-modification of ecosystem attractors therefore illustrates a mechanism that produces high-fitness biological complexes despite the fact that their evolution would seem highly implausible given the very small size of the basin of attraction that leads to this configuration under selection on the original units
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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